1. Field of the Invention
The present invention relates generally to epoxy end-capped oligomers derived from diolefin compounds, and a process for forming these oligomers, as well as to polymers formed from these oligomers and a process for forming such polymers. A particular feature of the present invention relates to an anionic telechelic process for forming the previously mentioned oligomers.
2. Description of the Background Art
Epoxy resins are widely used as adhesives, encapsulants, and coatings for a variety of applications. In particular, for application to structural and electronic devices, epoxy resins are useful since they provide mechanical protection, good substrate adhesion, thermal and oxidative stability, and moisture and solvent resistance. In addition, compliance is a highly desirable property for these resins since it allows the dissipation of stress that accompanies thermal and mechanical cycling of the encapsulant. Furthermore, enhanced toughness provides mechanical protection against fracture damage. However, state of-the-art systems exhibiting such compliance generally possess poor thermal stabilities. Another important property is the repairability of the adhesive, coating, or encapsulant. As expected, a rigid system is generally more difficult to repair and replace than a ductile one. Finally, as a practical matter, epoxy resins should have low viscosity and good handleability.
One particular type of epoxy compound which has been of interest in the past has been a epoxidized polybutadiene since polybutadiene has desirable flexibility properties. In the preparation of such epoxidized polybutadiene, as indicated, for example, by Lee and Neville, in the book entitled "Handbook of Epoxy Resins," Mc Graw-Hill Book Company, New York, 1967, at pages 3-14 to 3-15, and particularly the formula at page 3-15, butadiene is polymerized and the polybutadiene is subsequently epoxidized. However, in such a process, the epoxidizing agent randomly attacks the vinyl groups along the polybutadiene chain. Another type of epoxy compound of recent interest is an epoxidized polyisobutylene. One method for preparing an epoxidized polyisobutylene comprises the cationic polymerization of gaseous isobutylene and the reaction of the resultant polyisobutylene with meta-chloroperoxy benzoic acid to epoxidize the terminal groups, as described, for example, by J. Kennedy et al in the publication entitled "New Telechelic Polymers and Sequential Copolymers by Polyfunctional Initiator Transfer Agents (Inifers). XVIII. Epoxy and Aldehyde Telechelic Polyisobutylenes," in the Journal of Polymer Science: Polymer Chemistry Edition, Vol. 20, 1982 pages 2809-2817. However, in such a process, only the terminal groups on the polyisobutylene are epoxidized. As disclosed by Kennedy et al, telechelic polymers that bear reactive end groups have been used in the preparation of block and/or graft copolymers. The term "telechelic polymers" is used in the art to refer to polymers having two ionic ends by which the polymer growth can be continued, thus giving rise to the alternate name "living polymer". Such "living" polymers are generally described in U.S. Pat. No. 3,458,491 to K. S. Dennis. In addition, the latter patent also describes an anionic polymerization and termination process in which: (1) a diolefin monomer is reacted with a catalyst to form a polymer having negatively charged end groups; and then (2) the polymer is reacted with an external terminating agent to form a polymer having at least 80 percent of the end groups thereof derived from the external terminating agent. In such a process, the "living" polymer is not difunctional and, thus, is not a telechelic polymer. Moreover, the terminating agent adds only to the end groups on the polymer. The basic polymer is formed by free-radical polymerization which cannot be controlled, thus leading to uncontrollable results.
Thus, a need exists for an epoxy resin for electronic and structural applications which is tough, thermally and oxidatively stable, repairable, resistant to moisture and solvents, has good processing characteristics, and can be controlled in its structure.